This invention relates to a mass spectrometer and in particular to a mass spectrometer suitable for the secondary ion mass spectrometry (hereinbelow abbreviated to SIMS) for analyzing specimens developed on a thin layer chromatogram (hereinbelow abbreviated to TLC) plate. Here SIMS means the mass spectrometry of secondary ions emitted from a target irradiated with a primary ion beam or a neutral particle beam.
Recently TLC/SIMS is utilized for analyzing specimens developed on a TLC plate according to SIMS. Some examples concerning the summary of this method are described in the preprint of the joint discussion meeting of the Mass Spectrometry Society of Japan 1985, p. 148-p. 151.
According to the measurement method, when specimens developed on a TLC plate are sampled, at the moment where the plate is forwarded, collection of data is stopped and at the moment where the forwarding of the plate is stopped, the collection of data is started again. Data of peaks of a spectrum on a chromatogram are obtained continuously by repeating the steps described above.
According to the prior art techniques, data collection is started with the timing, where the forwarding of the plate is stopped (in practice the magnetic field for obtaining the mass spectra is swept). The states, where the plate is irradiated with a primary ion beam and secondary ions are emitted, when the plate is forwarded and when it is stopped, are naturally different and emission of secondary ions is stable only after a certain time has lapsed from the stopping of the plate. This is because the state of the matrix of glycerol, etc. is changed by primary ions projected to the plate and thus, when the plate is forwarded, new matrices are succeedingly irradiated so that there is no time for the matrix effect to achieve a steady state. Here the matrix effect means the action of the matrix to alleviate the shock produced by energy of primary ions, the action of the matrix to repair destroyed matrix owing to the viscosity of the matrix, etc. In order to have a steady matrix effect, it is necessary that a determined matrix state is irradiated with a primary ion beam during a certain period of time. Consequently, in order to obtain a stable mass spectrum, it is necessary to collect data, starting from a point of time, where the matrix effect achieves a steady state.